Pull out the dominoes seen above. Turn over. Shake up.
Ask the player to draw:
- No doubles ~70%
- Either Double ~ 30 %
- Double Blank ~15%
I like that it is simple, but seems more dramatic than dice (everything is a die roll but he was petitioning his god!). And it seemed pretty easy for him to understand the likelihood of success, in a way it might not if I said "Roll a 1-3 on this d4, next time you'll need to roll a 1-2 on a d6."
You can mess with the domino pool you're drawing from, but keep in mind it takes space to shake those things around ( I think 7 is the limit) and that I picked the blanks because they are simpler, and visually easier to read.